DC motor brush filter circuit
The present invention provides a motor control circuit including a motor with a motor winding and a brush, a battery, a relay, and a ground return circuit. The battery is for energizing the motor. The relay selectively provides connection between the battery and the motor. A ground return circuit is in communication with the brush. The ground return circuit creates a path from the brush through the relay to an electrical ground.
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The present invention claims priority to U.S. Provisional Application Ser. No. 60/415,890 filed on Oct. 3, 2002, entitled “DC Motor Brush Filter Circuit.”
TECHNICAL FIELDThis invention relates to systems and methods for suppressing electrical noise created by DC permanent magnet motors.
BACKGROUNDDesigns that use DC permanent magnet motors often make use of filters to eliminate noise from arcing caused by the commutation of the brushes in the motor. Generally a LC low pass filter is used to address the noise issue. In this filter configuration an inductance is placed in series between the switched power feed to the motor and the brush and a capacitor is placed from the switched power feed to ground. This filter topology is effective at filtering brush noise when the motor is running. However, due to the capacitance from the switched power feed to ground and the associated inrush current, this filter configuration can create excessive stress on relays used to control the motor. Moreover, a “pop” in the AM radio each time the motor is switched may result. In cases where the power to the motor is switched often, such as in the operation of intermittent windshield wipers, a repetitive “popping” noise in the AM radio may result. The strength of the “popping” depends on the positioning of the vehicle antenna with respect to the motor and the motor wiring harness, the radio and the strength of the station being received. Intermittent wipers can switch as often as once every two seconds so the “popping” may be unacceptable.
Since the problem is caused by current surges through the wiper wiring harness to support charging of the capacitors in the filter network as well as arcing due to the inductive nature of the motor load, a typical countermeasure has been to reduce the size of the filter capacitors or insert series resistance. The use of either of these methods will cause an increase in brush noise and Electromagnetic Interference (EMI). Typically a balance is struck between acceptable levels of brush noise and AM radio pop. If the level of noise is unacceptable more expensive semiconductor designs that allow current surges to be controlled are used.
Therefore there is a need for a new and improved system and method for suppressing brush noise. The new system and method should eliminate the capacitor surge current but retain the effectiveness of the filter for suppressing brush noise and EMI.
SUMMARYThe present invention solves the problems not addressed by the prior art by repositioning all of the filter capacitors in the LC filter such that there is effectively no capacitance between the switched power feed and ground but there is still an AC path to ground for the brush noise when the relay is closed to operate the motor. The end result is great reduction or elimination of AM radio popping in conjunction with reduced brush noise. Degradation of the switching relay contacts caused by the capacitor charge/discharge current is also eliminated. The new design of the present invention is most effective when the relay to control the motor is located adjacent to the motor, as in integrated wiper control modules, this allows the EMI radiating loop to be kept small.
The present invention provides a motor control circuit including a motor with a motor winding and a brush, a battery, a relay, and a ground return circuit. The battery is for energizing the motor. The relay selectively provides connection between the battery and the motor. A ground return circuit is in communication with the brush. The ground return circuit creates a path from the brush through the relay to an electrical ground.
In yet another embodiment of the present invention, the ground return circuit further includes a capacitor connected at a first end to the relay and at a second end to the electrical ground.
In yet another embodiment of the present invention, comprising a first filter circuit in communication with the brush, wherein the first filter circuit includes an inductor in electrical series connection with the capacitor.
In yet another embodiment of the present invention, the first filter circuit further comprises an inductor in electrical series connection with a capacitor. The capacitor is in electrically parallel connection with the ground return circuit.
In yet another embodiment of the present invention, the motor has a plurality of brushes and the first filter circuit is in communication with at least two of the plurality of brushes.
In still another embodiment of the present invention, wherein the first filter circuit is connected to a first and second brush of the plurality of brushes, the first filter circuit including a first and second inductor, a first end of the first inductor is connected to the first brush, a first end of the second inductor is connected to the second brush, where a capacitor is connected between the second end of the first and second inductors.
In still another embodiment of the present invention, wherein the first filter circuit is in electrical series connection with the ground return circuit.
In yet another embodiment of the present invention, the motor includes a common brush. The motor control circuit includes a second filter circuit in communication with the common brush, the second filter circuit creating a common brush ground path from the common brush to the electrical ground.
In yet another embodiment of the present invention, wherein the second filter circuit comprises an inductor in series with a capacitor.
In another embodiment of the present invention, a method is provided for filtering brush noise of a motor. The motor includes a winding and a brush. The steps of the method include selectively connecting the battery with the motor, energizing the motor, filtering the brush noise, providing a ground path through the relay, and providing a reservoir to supply surge current when the motor is energized.
In yet another embodiment of the present invention, wherein filtering the brush noise included providing the first filter circuit in electrical series connection with the ground path.
In yet another embodiment of the present invention, wherein providing the ground path includes connecting a capacitor between the relay and the electrical ground.
In still another embodiment of the present invention, wherein providing the reservoir to supply a surge current includes connecting a capacitor between the relay and the electrical ground.
In a further embodiment of the present invention, wherein the motor has a common brush, the method further comprising the step of filtering the brush noise of the motor using a second filter circuit, wherein the second filter circuit is connected between the common brush and an electrical ground.
These and other aspects and advantages of the present invention will become apparent upon reading the following detailed description of the invention in combination with the accompanying drawings.
Now referring to
Filters 10, 10′, 10″ work by shunting the noise (as indicated by paths P1, P2) generated by brushes 18, 28, and 34 back to the motor 39, as shown in
Unfortunately, the typical prior art approaches (shown in
Referring now to
In another aspect of the invention shown in
The design of circuits to suppress brush noise in DC permanent magnet motor applications is particularly challenging in applications where the motor is periodically switched on and off. Intermittent windshield wipers are an example of this type of application. There are several noise sources that must be suppressed in this situation each with conflicting requirements. The noise sources include broadband brush commutation noise and intermittent popping sounds caused by current surges associated with capacitor charging and relay contact arcing. In cases where the control circuitry can be located at the motor, the filter topology of the present invention satisfies the multiple conflicting constraints simultaneously, resulting in much improved noise reduction performance.
As any person skilled in the art of DC motor design will recognize from the previous detailed description and from the figures and claims, modifications and changes can be made to the preferred embodiments of the invention without departing from the scope of this invention defined in the following claims.
Claims
1. A motor control circuit comprising:
- a motor having a motor winding and a plurality of brushes;
- a first filter circuit connected to a first and second brush of the plurality of brushes, wherein the first filter circuit has a first and second inductor and a capacitor, and wherein a first end of the first inductor is connected to the first brush, a first end of the second inductor is connected to the second brush, and the capacitor is connected between the second end of the first and second inductors;
- a battery in communication with the motor for energizing same;
- a relay in selective communication with the battery and the first filter circuit for selectively providing battery power to the motor;
- a ground return circuit in communication with at least one of the plurality of brushes, wherein an electrical return path is created through the relay from the at least one brush back to the motor; and
- a second filter circuit in communication with a third brush, wherein the third brush is a common brush, the second filter circuit creating a common brush ground path from the common brush to an electrical ground, and wherein a second filter circuit includes an inductor in series with a capacitor.
2. The motor control circuit of claim 1, wherein the ground return circuit further comprises a ground return capacitor connected at a first end to the relay and at a second end to an electrical ground.
3. The motor control circuit of claim 1, wherein the first filter circuit includes a second capacitor connected to ground.
4. The motor control circuit of claim 1, wherein one of the first and second inductors is in electrical series connection with the capacitor.
5. The motor control circuit of claim 4, wherein the capacitor of the first filter circuit is in electrically parallel connection with the ground return circuit.
6. The motor control circuit of claim 3, wherein the motor has three brushes and the first filter circuit is in communication with at least two of the three brushes.
7. The motor control circuit of claim 1, wherein the first filter circuit is in electrical series connection with the ground return circuit.
8. A method for filtering brush noise of a motor, the motor having a winding and a plurality of brushes, the method comprising:
- connecting a battery selectively with the motor using a relay connected between the battery and the motor;
- energizing the motor by selectively connecting the battery with the plurality of brushes of the motor;
- filtering the brush noise of the motor using a first and second filter circuit, wherein the first filter circuit is connected to a first and second brush of the plurality of brushes, wherein the first filter circuit has a first and second inductor and a capacitor, and wherein a first end of the first inductor is connected to the first brush, a first end of the second inductor is connected to the second brush, and the capacitor is connected between the second end of the first and second inductors, and wherein the second filter circuit is in communication with a common brush to create a common brush ground path from the common brush to an electrical ground, and wherein the second filter circuit includes an inductor in series with a capacitor;
- providing a return path through the relay from at least one of the plurality of brushes back to the motor; and
- providing a reservoir to supply a surge current to the first filter circuit when the motor is energized, thereby eliminating electromagnetic interference caused by the surge current between the battery and the relay.
9. The method of claim 8, wherein filtering the brush noise includes providing the first filter circuit in electrical series connection with the return path.
10. The method of claim 8, wherein providing the return path includes connecting a ground return capacitor between the relay and an electrical ground.
11. The method of claim 8, wherein providing the reservoir to supply a surge current includes connecting a ground return capacitor between the relay and an electrical ground.
12. The method of claim 8, wherein the motor has a common brush, the method further comprising the step of filtering the brush noise of the motor using a second filter circuit, wherein the second filter circuit is connected between the common brush and an electrical ground.
4217526 | August 12, 1980 | Farr |
4329605 | May 11, 1982 | Angi et al. |
4429241 | January 31, 1984 | Ohara et al. |
4734601 | March 29, 1988 | Lewus |
4795951 | January 3, 1989 | Gaebel et al. |
4829230 | May 9, 1989 | Perry |
4853569 | August 1, 1989 | Lewus |
5196750 | March 23, 1993 | Strobl |
5231321 | July 27, 1993 | Takiguchi |
5289089 | February 22, 1994 | Aoki |
5306974 | April 26, 1994 | Bates |
5402045 | March 28, 1995 | Mori |
5525878 | June 11, 1996 | Buchanan et al. |
5811948 | September 22, 1998 | Sato et al. |
5838877 | November 17, 1998 | Elliot et al. |
5869942 | February 9, 1999 | Miller et al. |
5937506 | August 17, 1999 | Nakata |
5942819 | August 24, 1999 | Burgess et al. |
6078117 | June 20, 2000 | Perrin et al. |
6717301 | April 6, 2004 | DeDaran et al. |
0 608 581 | August 1994 | EP |
2 217 136 | October 1989 | GB |
Type: Grant
Filed: Apr 23, 2003
Date of Patent: Aug 16, 2005
Patent Publication Number: 20040066157
Assignee: Visteon Global Technologies, Inc. (Dearborn, MI)
Inventors: Gary E. Zack (Novi, MI), Charlie Richlie (Northville, MI)
Primary Examiner: Rina Duda
Assistant Examiner: Patrick Miller
Attorney: Brinks Hofer Gilson & Lione
Application Number: 10/421,686